Kyle Edmund was knocked out of the Erste Bank Open 500 in Vienna by Spain's Fernando Verdasco.
The British No 1 won the European Open in Antwerp on Sunday for his first trophy on the main tour and followed it up with a fine first-round win over Diego Schwartzman.
But his hopes of going deep in the Austrian capital suffered a blow as went down 6-4 3-6 6-3 in a close encounter to the experienced left-hander Verdasco after one hour and 55 minutes.
The Spaniard, who like Edmund has had a fine season, had the better of three breaks to start the match and held on to take the opening set.
Verdasco proved just the stronger in a close encounter
Edmund hit back well, breaking serve at the start of the second and levelling the match, but one break proved the difference in the decider and it is Verdasco who moves through to a quarter-final with either Gael Monfils, who defeated American fourth seed John Isner 6-4 6-4.
Edmund heads to Paris for the final Masters tournament of the season, which he would need to win to give himself a chance of qualifying for the ATP Finals in London.
In other matches, Japanese fifth seed Kei Nishikori eased past Karen Khachanov 6-2 6-2, while Kazakhstan's Mikhail Kukushkin defeated a tempestuous Andrey Rublev 7-6 (7-4) 6-4 and home favourite Dominic Thiem overcame Sam Querrey 6-4 6-4.
Elsewhere, Roger Federer won his 17th straight match at the Swiss Indoors in Basel to maintain his bid for a ninth title at his hometown event.
Roger Federer has reached the Basel final in his last 11 appearances
The 20-time Grand Slam champion recovered from a break down in the first set against Jan-Lennard Struff to progress 6-3 7-5 and will next meet Gilles Simon, who beat Ernests Gulbis 7-6 (7-4) 7-6 (7-0).
Alexander Zverev also moved through to the quarter-finals as the German second seed ended the run of Russian qualifier Alexei Popyrin 6-4 6-4 and he will next face Roberto Bautista Agut after the Spaniard earned a comeback 6-7 (6-8) 6-3 6-3 win.
Stefanos Tsitsipas dominated Peter Gojowczyk 6-3 6-1 to line up a Swiss Indoors quarter-final with one of his toughest NextGen rivals.
Stefanos Tsitsipas set up a meeting with Daniil Medvedev in Basel
The Greek fourth seed will next face Russian Daniil Medvedev, who defeated Italy's Andreas Seppi 7-6 (7-5) 6-2 in their second-round encounter in Basel.
Tsitsipas made his trophy breakthrough at the weekend in Sweden with his first career title.
"I'm playing well," said 16th-ranked Tsitsipas, who moved onto 41 victories for the season. "I think the rivalry between the young guys right now may be even stronger than that of the big names.
"We all want to get to the top sometime, we always want to do better than the other guy."